The cytochrome P450 isoenzyme CYP1A1 is intimately involved in the metabolic activation of pulmonary procarcinogens and its expression is induced by components found in tobacco smoke condensate. The CYP1A1 gene has been implicated as a risk factor in the etiology of lung cancer in heavy cigarette smokers. The role of human CYP1A1 in lung carcinogenesis was analyzed at the level of: A. General regulatory patterns in neoplastic and non-neoplastic lung. Oligonucleotide directed mutagenesis (ODM) of numerous potential transcriptional elements within the regulatory region of the human CYP1A1 gene was carried out. Using a panel of well characterized human non-small cell lung cancer (NSCLC) cell lines, we have identified a unique pattern of expression of the CYP1A1 gene that requires interaction with two copies of the transcriptional activator known as the aromatic hydrocarbon receptor at two widely separated DNA regulatory elements. B. Activator-repressor interactions. Elucidation of the pattern of expression of the human CYP1A1 gene involving two transcriptional activators has stimulated additional studies on the potential role of a transcriptional repressor or "silencer." C. Feedback modulation. In certain mutant murine derived hepatoma cell lines, the CYP1A1 gene product, aromatic hydrocarbon hydroxylase (AHH) was shown to play an autoregulatory role in CYP1A1 gene expression. We are investigating the possibility that, in some NSCLC lines, the elevated basal levels of CYP1A1 gene expression observed may be due to a similar mechanism. D. Proto-oncogene interaction. Preliminary studies have identified a potential interaction between the regulatory region of the CYP1A1 gene and the proto-oncogenes c-fos and c-jun. The significance of the project is to elucidate the interactive role of genetically determined factors and chemical carcinogens in pulmonary carcinogenesis. The results will have diagnostic and prevention applications.